This invention pertains generally to pressure molding of fluid materials and particularly using light energy to cure such materials. It also pertains to molds fabricated from self curing optically clear materials so that fluid materials cured with light energy may be used in conjunction with such molds.
Various types of dental restorative materials that use light energy to change from a plastic state to a fused or “cured” state are used in dentistry. These materials may either be placed incrementally in the tooth and cured in layers or fabricated in the laboratory on a model made from an impression taken in the patient's mouth.
In the first instance where the curing takes place in the patient's mouth, control becomes a problem. Such control incorporates ability to maintain a dry field, to completely cover all the prepared tooth surface (close the margins), maintain a homogeneous material layer without incorporating spaces which have no restorative material, proper contact, contour size, shape, occlusal harmony and depth of cure to name a few. The advantages are that it is quick, has a reasonable success rate and is of moderate expense. It satisfies the patient's desire for an aesthetic restoration.
In the second instance the indirect method which requires a model made from an impression allows for complete control over the size, shape, contour, contact, shade and occlusal harmony to name a few. The disadvantages are that the model is completely dependant upon an accurate impression, an accurate stone model (no bubble, cracks, etc.), requires more time for fabrication and is much more costly.
In both instances, shrinkage of the material must be taken into consideration. In each case the material does not cure at the surface (an oxygen inhibited layer). In the first instance complete curing by tempering is not possible while in the second instance heat tempering (200-250 degrees F. for 15 minutes) gives the laboratory fabricated restoration more strength.
Laboratory fabricated composite resin inlays and/or crowns are usually assembled in an incremental fashion by placing small amounts of the appropriate colored composite in or on the stone die and light curing it followed by an additional increment until the proper configuration is accomplished. Notwithstanding the care with which the material may be placed, there is always a difference in the cure and coverage of the material in the incremental method. In addition clear modeling resins are used to prevent the instruments from sticking to the resin and ensure one layer sticks to the other. All manufacturers advise using only small amounts of the fluid as it has the tendency of reducing the strength of the cured material. This method is cured from the inside out. The light source is unidirectional and as a consequence the shrinkage is away from the margins and die surface. It requires that a separating material be placed on or in the model such that the partially cured material may be removed without breaking or mutilating the die. It is not desirable to remove the restoration prior to completion in this method as it never reseats accurately. Consequently the thickness of the restoration cannot be verified prior to curing. Spacer thickness creates a problem when the restoration is to be placed in the mouth and cured. The American Dental Association has specifications regarding cement thickness for all types of restorations. The spacer thickness cannot be controlled to a degree such that there is a reproducible specified space between the restoration and the tooth.
An additional problem with the above method is that to generate occlusal harmony, the finished product must be ground and fitted to the die. This has the problem of possible fracture or changing of the die. The laboratory technician must be extremely careful in the fabrication. Also if the shade of the restoration has to be changed, the die then becomes used again where fracture can be a problem.
Many patents have been granted whereby the materials used for the fabrication laboratory restorations are subjected to various methods to strengthen them. Vacuum, pressure under nitrogen or water, and heat are just some of them. Those methods have been used singularly or in combination. In most instances they have met the test inventors' intentions.